The present invention relates to an oxidation catalyst, an oxidation process using the same, and a process for producing ketoisophorone from xcex2-isophorone.
Ketoisophorone (4-oxoisophorone), a useful intermediate for a starting material of medicines, perfumes, condiments, and for polymer, is produced from isophorone and the like. For example, as a process for producing 4-oxoisophorone by oxidizing xcex2-isophorone with oxygen, there have been proposed a method in which xcex2-isophorone is oxidized with oxygen in the presence of a phosphomolybdic acid or a silicomolybdic acid [Japanese Patent Publication No. 30696/1980 (JP-B-55-30696)], a method in which xcex2-isophorone is oxidized with oxygen in the coexistance of a phosphomolybdic acid or a silicomolybdic acid and an alkaline metal compound or an aromatic amine [Japanese Patent Application Laid-Open No.191645/1986 (JP-A-61-191645)], and a method in which xcex2-isophorone is oxidized with oxygen in the presence of a vanadium catalyst [Japanese Patent Application Laid-Open No. 93947/1975 (JP-A-50-93947)]. Japanese Patent Application Laid-Open No. 81347/1974 (JP-A-49-81347) discloses a method for producing 4-oxoisophorone by oxidizing xcex2-isophorone with an alkaline metal chromic acid salt or a dichromate or a chromium trioxide. In the Chem. Lett. (1983), (7), 1081, there is disclosed a method for producing 4-oxoisophorone by oxidizing xcex2-isophorone using t-butylhydroperoxide in the presence of a palladium catalyst. However, in these methods, the selectivity of ketoisophorone is reduced, therefore separation of the formed by-product(s) or a metal catalyst and purification of the object compound are complicated. Moreover, these methods involve using a heavy metal compound requiring special treatment, such as chromium, or a peroxide needed to be handled with care, which results in a decrease in working efficiency.
Moreover, as a method for producing ketoisophorone from xcex2-isophorone, Japanese Patent Application Laid-Open No. 125316 (JP-A-51-125316) discloses a method for producing an ethylenically unsaturated dicarboxylic acid by oxidizing xcex2-ethylenically unsaturated ketone with molecular oxygen or a molecular oxygen-containing gas in the presence of an inorganic base or an organic base and a cobalt or manganese chelate. In this method, however, the yield of ketoisophorone is low due to the use of a straight-chain secondary or tertiary amine such as triethylamine as the organic base.
In Japanese Patent Application Laid-Open No. 53553/1998 (JP-A-10-53553) discloses a method for producing ketoisophorone by oxidizing xcex2-isophorone with molecular oxygen in the presence of bis(2-hydroxybenzylidene)-ethylenediamine-manganese complex salt (i.e., manganese-salene), an organic base, a specific substance having a catalytic action (e.g., acetylacetone), and water. In the literature, there is recited as the manganese complex salt a complex in which 1 mole of bis(2-hydroxybenzylidene)-ethylenediamine is coordinated relative to 1 mole of manganese. However, even in the above method using the above manganese complex salt, the conversion and the selectivity of a substrate are not improved enough. Particularly, a higher concentration of xcex2-isophorone in the reaction system causes a considerable decrease in the yield of ketoisophorone. For example, when the concentration of xcex2-isophorone is 20% by weight or more, the conversion and/or the selectivity is decreased to a large extent. Therefore, relatively large amounts of a manganese complex salt and an organic base are required for an improved conversion. Further, a lower concentration of oxygen remarkably decreases the reaction rate.
Thus, an object of the present invention is to provide an oxidation catalyst capable of oxidizing a substrate with high conversion and high selectivity regardless of the concentration of the substrate, and an oxidation process using the same.
Another object of the present invention is to provide an oxidation catalyst capable of oxidizing a substrate with high conversion and high selectivity even used in a catalytic amount, and an oxidation process using the same.
Further object of the present invention is to provide an oxidation catalyst which ensures the efficient proceeding of an oxidative reaction efficiently proceeds even with, as a source of molecular oxygen, a low oxygen content gas, such as air, and an oxidation process using the same.
Still further object of the present invention is to provide an oxidation catalyst capable of producing ketoisophorone with maintaining high conversion and high selectivity even with a high xcex2-isophorone concentration and a low oxygen concentration, and a process for producing ketoisophorone using the same.
The inventors of the present invention did intensive investigations to achieve the above objects and found that, even in a reaction system with a high substrate (e.g., xcex2-isophorone) concentration and a low oxygen concentration, the substrate can be oxidized with high conversion and high selectivity by using a specific complex comprising manganese and an N,Nxe2x80x2-disalicylidenediamine, and that the conversion and the selectivity are remarkably improved by further employing or incorporating a basic nitrogen-containing compound in combination with the above complex. The present invention was accomplished based on the above findings.
Accordingly, the oxidation catalyst of the present invention comprise (1) a crystalline complex of manganese with an N,Nxe2x80x2-disalicylidenediamine, or (2) the above complex (1) and a basic nitrogen-containing compound. The melting point of the above crystalline complex may be about 190 to 240xc2x0 C.
The present invention further includes an oxidation process in which a substrate is oxidized with oxygen in the presence of the above oxidation catalyst, for example, a process which comprises oxidizing xcex2-isophorone or a derivative thereof with molecular oxygen to produce a corresponding ketoisophorone or a derivative thereof.
In the specification, the term xe2x80x9cN,Nxe2x80x2-salicylidenediaminexe2x80x9d is taken to mean that an N,Nxe2x80x2-salicylidenediamine may have a structure in which a salicylidene group is bound to a nitrogen atom of each amino group of an aliphatic, alicyclic, or aromatic diamine.